Conventionally, as a method of generating a hydrogen gas by a reaction of water and aluminum, a method of reacting water and aluminum while a new surface of aluminum is produced by cutting it in water has been known (for example, see Japanese Patent Application Laid-Open No. 2001-31401).
However, according to this method, since new surfaces and fine particles of aluminum are successively produced, it was difficult to control a rate of reacting water and aluminum. In addition, unless heating is performed from the outside, a reaction rate becomes insufficient, and there is also a problem of heating controlling.
In addition, a method of supplying water to a powder in which an aluminum powder and a metal powder having smaller ionization tendency are mixed so as to react water and aluminum has been known (for example, see Japanese Patent Application Laid-Open No. 2002-104801). In this method, by mixing the metal powder having smaller ionization tendency than that of aluminum, an apparent rate of reacting water and aluminum can be enhanced.
Further, as a hydrogen generating composition which can stably produce hydrogen at a normal temperature, a hydrogen generating composition containing an aluminum powder and a calcium oxide powder in which a ratio of the aluminum powder is 85% by weight or less per 100% by weight of the sum of the aluminum powder and the calcium oxide powder, has been known (for example, Japanese Patent Application Laid-Open No. 2004-231466). And, as an aluminum powder, the powder having a particle size distribution of 50 to 150 μm is preferably used.
However, in this hydrogen generating composition, since a content of calcium oxide is large, calcium oxide is converted into calcium hydroxide by a reaction with water, an amount of a produced calcium ion is increased, therefore, it is hardly said that this is a suitable method as a method of generating a hydrogen gas to be supplied to a fuel cell. That is, it was found out that when an amount of a produced calcium ion is increased, a large amount of the ion is contained in water contained in a produced hydrogen gas, the calcium ion together with a hydrogen gas reaches a solid electrolyte of a fuel cell, and causes a problem of suppression of proton conducting function.
On the other hand, in a hydrogen generating composition containing aluminum as a main component, it was found out that, when aluminum oxide is produced by progression of a reaction, aggregation and solidification of reaction products are easily caused, aluminum particles are shut therein, and a reaction yield is lowered. And, such the aggregation and solidification phenomenon becomes remarkable as a particle diameter of aluminum particles is smaller.